Electric cars, which have near-silent engines, will need to have noise-making devices installed to let people know they are near, under a US government proposal.

Sounds would need to be detectable when vehicles were travelling slower than 29km/h so electric and hybrid-electric cars could be heard by cyclists and pedestrians, particularly the visually impaired, under the US National Highway Traffic Safety Administration rule.

The rule, which would have to be made final before it takes effect, would save 35 lives over each model year of hybrid vehicles and prevent 2,800 injuries, the agency said.

"To add about a US$30 or US$35 item to a car for this kind of injury and death prevention, it's hard to argue against," said Jesse Toprak, an analyst for industry data provider TrueCar.com in Santa Monica, California. "I'm sure all of us have experienced at some time the fear of getting struck by a Prius."

Adding external speakers to quiet vehicles would cost about US$25 million a year, or about US$35 per light vehicle, the safety agency said.

Toyota, maker of the Prius, already equipped its hybrid cars sold in Japan with a noise-maker, even though Japan had no such regulations, said Shino Yamada, a Tokyo-based spokeswoman for Asia's largest carmaker.

"Our proposal would allow manufacturers the flexibility to design different sounds for different makes and models while still providing an opportunity for pedestrians, bicyclists and the visually impaired to detect and recognise a vehicle and make a decision about whether it is safe to cross the street," the administrator of the safety agency, David Strickland, said.

Quiet cars are twice as likely as other vehicles to be involved in pedestrian accidents when backing up, slowing or stopping, starting in traffic or entering or leaving a driveway, a 2011 study found.

This article appeared in the South China Morning Post print edition as US plan for quiet cars to speak up to cut pedestrian toll